Soil decontamination

Only two processes, high-temperature pyrolysis and mobile incineration, have proved effective for soil decontamination and are considered to be commercially viable. Both involve heating the contaminated soil to a high temperatnre, which is costly in terms of energy use and materials handling. There are substantial opportunities for innovation and development of processes for the separation of eontaminants from soils and the in-situ treatment of contaminated soils. Examples of each are given in the following subsections. 

Vasilyeva, G.K. Kreslavski, V.D. Oh, B.T. Shea, P.J. Potential of activated carhon to decrease 2,4,6-trinitrotoluene toxicity and accelerate soil decontamination. Environ. Toxicol. Chem. 2001, 20, 965-971. 

The Advanced Recovery Systems, Inc. (ARS) soil washing technology is an ex situ soil decontamination process for decontaminating radioactively contaminated soil. ARS developed the technology to treat contaminated soil. 

Aqueous biphasic systems offer the potential for highly selective and low-cost separations. Aqueous biphasic extraction for soil decontamination is based on the selective partitioning of either dissolved solutes or ultrafine particulates between two immiscible aqueous phases. Both soluble and particulate uranium contaminants can be separated from soil using this technique. Aqueous biphasic extraction may also have application for separation of plutonium and thorium from soil or waste. 

Aqueous biphasic systems have been used commercially for protein separations, separation of metal ions, ultrafine particles, and organics. Application of the technology for soil decontamination has only been demonstrated in laboratory-scale studies. 

Lynntech, Inc. s (Lynntech s), electrokinetic remediation of contaminated soil technology is an in situ soil decontamination method that uses an electric current to transport soil contaminants. According to Lynntech, this technology uses both direct current (DC) and alternating current (AC) electrokinetic techniques (dielectrophoresis) to decontaminate soil containing heavy metals and organic contaminants. A non homogeneous electric field is applied between electrodes positioned in the soil. The field induces electrokinetic processes that cause the controlled, horizontal, and/or vertical removal of contaminants from soils of variable hydraulic permeabilities and moisture contents. 

The electrochemical soil decontamination process is designed to treat organic compounds and heavy metals. It utilizes induced electrical currents to establish chemical, hydraulic, and electrical gradients designed to extract contaminants for soils. Treatment may be accomplished in situ or on site in lined cells. 

The studies with sediment cultures indicate natural degradation potential for aquatic sediments exposed to anthropogenic CP pollution. However, in situ remediation rates for CP-contaminated sediments may be difficult to enhance. Possibilities involve nutrient and electron donor/acceptor amendments. Ex situ remediation could involve sediment dredging and application of methods developed for soil decontamination, such as slurry reactors and composting. 

Radio frequency thermal soil decontamination (lubricants and solvents)... 

In 2002, an interesting concept was proposed for coupling a C02-based supercritical extraction with air oxidation in order to remove and decompose pollutants from gases or liquids (134). An exemplary process scheme according to this preliminary concept is shown in Figure 5. Possible (future) environmental applications of such an integrated supercritical extraction-reaction system include treatment of liquid effluents, regeneration of catalysts and adsorption materials, and soil decontamination. 

Dougherty, E.J., McPeters, A.L., Overcach, M.R. (1991) Kinetics of photodegradation of 2,3,7,8-tetrachlorodibenzo-p-dioxin theoretical maximum rate of soil decontamination. Chemosphere 23, 589-600. 

Fig. 15.30. Schematic of electrolysis, adsorp-tion/desorption, and electro-osmotic flow. (Reprinted from R. J. Gale, Soil Decontamination Using Elec-trokinetic Processing, in Environmental Oriented Electrochemistry, C. A. C. Sequeira, ed., Fig. 2, p.

Another very important green chemistry solvent is supercritical water (SCW) [14], Water under supercritical conditions is an extremely powerful oxidizing and cleansing agent that has been proven remarkably promising as a soil decontaminant by efficiently degrading persistent organic toxic wastes that are difficult to eliminate from polluted soils, and in the treatment of several types of industrial wastes such as textile and cellulose wastewater [2],... 

Supercritical fluid extraction has now found a lot of applications in different fields (polymers, aromas and essential oils, fats, natural products, soil decontamination...) and several production units are operated in agroalimentary (coffee, hop...) and pharmaceutical industries. In order to estimate the economical interest of these applications, technical and economical extrapolation methods have been developed. These methods are dependent of the nature of the extraction and are based on experimental results obtained on pilot plant units. We describe here a general extrapolation procedure, and a case study is presented to illustrate an economical estimation of a supercritical fluid extraction. 

Electroremediation using electrical current is the final purification method discussed in this chapter. Here, an array of anodes are placed in the soil opposite an array of cathodes. When electric potential is apphed the following processes occur electrolysis of water in the soil, dissolution of polluting ions, migration of ions under the influence of the apphed potential field, and reduction or pH based precipitation at the cathode [68,69]. This technique, also known as electroreclamation or electrochemical soil decontamination, does not require a membrane however, improved electroremediation has been reported when ion-exchange membranes were incorporated into the system [70]. The function of the membrane is to retain OH ions produced at the cathode. Migration of these OH ions is prevented to avoid precipitation of the heavy metal ions in the sod. 

S.I. Darmawan Wada, Effect of Clay Mineralogy on the Feasibility of Electro-kinetic Soil Decontamination Technology, Appl. Clay Sci. 20(6), 283-293, Eeb. (2002). 

Rotary kilns (e.g., cement kilns), metal-recovery and smelting furnaces, mobile incinerators, and industrial boilers are primarily used to incinerate hazardous wastes. The obvious benefits of combustion of waste as fuel are the recovery of energy from the waste and the conservation of fossil fuels. Because the kiln and furnace operators are paid to take in the waste, rather than having to pay for fuel, also create economic incentives. Mobile incinerators are most commonly used for soil decontamination projects, and can be moved from site to site once the job is completed. 

Ozone has been applied successfully and extensively for water and wastewater treatment. Ozone also has been used as a safe and effective antimicrobial agent in many food applications. Other applications of ozone include soil decontamination, polymer surface modification, and bleaching paper pulps. It is recognized that for water treatment, the combined use of ozone with either biological treatment, or heterogenous catalysts, or UV and/or H2O2 makes the whole process more efficient. 

The table of contents illustrates the breadth of this volume. About one-third of the chapters deal directly with remediation technologies for groundwater and soil decontamination another third deal with waste treatment avoidance technologies and the last third discuss fundamental research for developing new technologies or for measuring the problem or the effectiveness of the treatment. This book will provide a contribution to this important field and wilt reemphasize the need for continued progress and development. 

Assink, J.W. "Extractive Medrads for Soil Decontamination A General Survey and Review of Operational Treatment Installations," In Contaminated Soil Assink, J.W. van der Brink, W.J., Eds. Martinus Nijhoff Dmxlrecht, The Netherlands, 1986 pp. 655-. 

In this chapter, three applications at different stages of development will be presented in detail. Whereas the application in soil decontamination is still in the experimental phase,... 

Surfactants and microemulsion systems can be used for ex situ treatment of contaminated soil or in situ soil decontamination. In situ remediation is usually preferred if excavation of the contaminated soil is not possible or expensive, e.g. beneath buildings or for contaminations at great depth. Often bioremediation or natural attenuation is used for decontamination. In most cases, these techniques only permit the effective degradation of contaminants in the plume formed by dissolved pollutants which may be very large. However, for the remediation of a contaminated site, it is also necessary to remove the source where the pollutants maybe adsorbed in large quantities or may be present as solid or liquid phases. The latter are called NAPL (non-aqueous phase liquids) and a differentiation is made between LNAPL (light non-aqueous phase liquids) with a lower density than water and DNAPL (dense non-aqueous phase liquids) with a higher density than water (see Fig. 10.1). 

Preformed micro emulsions can also be used for soil decontamination. The application of bioremediation with microemulsions containing nutrients for oil spills is already a well-known technology [84, 85] and is also proposed for in situ treatment of DNAPL sites [86]. Studies on contaminant extraction, however, are less frequent. In most cases, these systems have been discussed and investigated for adsorbed or highly viscous contaminants which can only be solubilised. Enhancement of solubilisation in micro emulsions compared with surfactant solutions was found for pyrene [87] and patented for ex situ treatment of contaminated soil [88]. An interesting cost-effective variation uses partially sulphated castor oil [89]. 

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